Buonasera, potete confermarmi quanto scritto:
- Se sento un rumore involontario (rumore del traffico) e/o improvviso (il bicchiere che cade in salotto):
Did you hear it?
- Se stiamo parlando ma non sento cosa dici:
I didn't/ couldn't hear you, could you repeat please?
What did you say?
- Se stiamo parlando ma non capisco perchè non conosco bene la lingua:
Could you repeat please?
??? Pardon/Pardon me. ???
??? What did you say? ???
- Se non ti ho ascoltato di proposito:
I didn't listen to you.
To hear = Sentire
To listen = Ascoltare
But as to your questions:
1/ Did you hear it?
Di solito: "Did you hear THAT?" "It" would be used if you had already named the thing that you had heard; for example:
"I heard an explosion. Did you hear it?"
But if you haven't been specific you would say.
"Did you hear that?"
2/ I didn't/ couldn't hear you, could you repeat please?
Although this would be understood, you would normally say "could you repeat that, please" to identify exactly what it was that you wanted repeated. You could also be more specific like "could you repeat the last sentence?" However in either case you should really have a noun or pronoun identifying what you wanted to be repeated.
3/ Pardon/Pardon me.What did you say?
Yes, but you would always express it as a question. "Pardon?" or "Pardon me?" "Pardon" by itself is really an abbreviation of "I beg your pardon?"
4/ I didn't listen to you.
It's not wrong (if you are referring to one, specific instance) but it would be more common to say "I wasn't listening to you". In English that type of expression is closer to the imperfetto than to the passato prossimo.
With this sort of post, I recommend asking in the Answers section ( https://www.italki.com/questions ) rather than the Discussions one.